Many people know texting while driving increases crash risk. But cell phone conversation while driving is also risky. Talking on hands-free or handheld cell phones requires the brain to multitask – a process it cannot do safely while driving.

To explain what happens to the human brain when talking on cell phones while driving, NSC has a white paper, “Understanding the distracted brain: Why driving while talking on hands-free phones is risky behavior:”

Below is the article “Understanding the distraced brain: Why Driving while talking on hands-free phones is risky behavor:”

In January 2004, at 4:00 p.m., in
Grand Rapids, Michigan, a 20-yearold
woman ran a red light while talking
on a cell phone. The driver’s vehicle slammed
into another vehicle crossing with the green light
directly in front of her. The vehicle she hit was not the
first car through the intersection, it was the third or
fourth. The police investigation determined the driver
never touched her brakes and was traveling 48 mph
when she hit the other vehicle. The crash cost the
life of a 12-year-old boy. Witnesses told investigators
that the driver was not looking down, not dialing the
phone, or texting. She was observed looking straight
out the windshield talking on her cell phone as she
sped past four cars and a school bus stopped in
the other south bound lane of traffic. Researchers
have called this crash a classic case of inattention
blindness caused by the cognitive distraction of a
cell phone conversation.

Vision is the most important sense for safe driving.
Yet, drivers using hands-free phones (and those
using handheld phones) have a tendency to “look
at” but not “see” objects. Estimates indicate that
drivers using cell phones look but fail to see up
to 50 percent of the information in their driving
environment.1 Distracted drivers experience what
researchers call inattention blindness, similar to
that of tunnel vision. Drivers are looking out the
windshield, but they do not process everything
in the roadway environment that they must know
to effectively monitor their surroundings, seek
and identify potential hazards, and respond to
unexpected situations.2

Today there are more than 320 million wireless
connections in the U.S. And although public
sentiment appears to be turning against cell phone
use while driving, many admit they regularly talk
or text while driving. The National Highway Traffic
Safety Administration estimates that nine percent of
all drivers at any given time are using cell phones,
and the National Safety Council estimates about one
in four motor vehicle crashes involve cell phone use
at the time of the crash.

Cell phone distracted driving has become a serious
public health threat. A few states have passed
legislation making it illegal to use a handheld cell
phone while driving. These laws give the false
impression that using a hands-free phone is safe.
The driver responsible for the above crash was on
the phone with her church where she volunteered
with children the age of the young boy who lost his
life as the result of her phone call. She pled guilty to
negligent homicide and the lives of two families were
terribly and permanently altered. Countless numbers
of similar crashes continue everyday.

This paper will take an in-depth look at why
hands-free cell phone use while driving is dangerous.
It is intended that this information will provide
background and context for lawmakers and
employers considering legislation and policies.

Motor vehicle crashes are among the
top two causes of injury death throughout
a person’s lifetime.3 They also are the No. 1 cause
of work-related death.4 Annually, more U.S. soldiers are
killed in crashes in privately-owned vehicles than all
other Army ground casualties combined.

Each year since 1994, between 32,800 and 43,500
people have been killed in motor vehicle crashes.

That’s more than 737,000 lives lost during these years.
It includes people inside and outside of vehicles, as well
as motorcyclists, bicyclists and pedestrians who were
struck by vehicles. There are activities people tend to
think are riskier than driving, such as flying in an airplane,
but consider this: The lives lost on U.S. roadways each
year are equivalent to the lives that would be lost from a
100-passenger jet crashing every day of the year.

In addition to the thousands of fatalities, many more
people suffer serious life-changing injuries in motor
vehicle crashes. More than 2.2 million injuries resulted
from vehicle crashes in 2010.

To reduce this toll, prevention must focus on the top
factors associated with crashes. Driver distractions
have joined alcohol and speeding as leading factors
in fatal and serious injury crashes. The National Safety
Council estimates 21 percent of all crashes in 2010
involved talking on cell phones – accounting for 1.1
million crashes that year. A minimum of three percent of
crashes are estimated to involve texting.

Cell phone use has grown dramatically over the past 15
years. In 1996, cell phone subscriptions covered only
14 percent of the U.S. population; by 2011, that had
grown to 102.4 percent.

The National Highway Traffic Safety Administration
estimates that at any point during the day, nine percent
of drivers are using cell phones. More than two-thirds
of respondents to a AAA Foundation for Traffic Safety
survey reported talking on cell phones while driving during
the previous 30 days.11 Nearly one in three admitted they
engaged in this behavior fairly often or regularly.

Because text messaging has grown dramatically – an
almost 10,000-fold increase in 10 years – and because
there is already near-public consensus that it’s a
serious driving safety risk, texting receives a great deal
of attention. More than one-third of people admitted
to reading a text or email while driving in the past 30
days, and more than one-quarter admitted to sending
a text or email.12 Although texting is clearly a serious
distraction, NSC data show drivers talking on cell
phones are involved in more crashes. More people are
talking on cell phones while driving more often, and
for greater lengths of time, than they are texting. Thus,
in 2010, an estimated minimum of 160,000 crashes
involved texting or emailing, versus 1.1 million crashes
involving talking on cell phones.

Cell phone distracted driving has captured the attention
of nation’s political leaders and employers and they are
taking action:

-In December 2011, the National Transportation
Safety Board recommended that all 50 states
and the District of Columbia enact complete bans
of all portable electronic devices for all drivers –
including banning use of hands-free devices.

– While no state yet prohibits all drivers from any
cell phone use, as of March 2012, 31 states
prohibit teen drivers from any cell phone use,
including handheld and hands-free.

– The Federal Government has taken action.
President Barack Obama issued an Executive
Order banning federal employees from texting
while driving. Rules about employee use of cell
phones while driving have been issued by the
Occupational Safety and Health Administration,
Federal Motor Carrier Safety Administration and
Federal Railroad Administration.

– A National Safety Council membership survey
showed employers of all sizes, sectors and
industries are implementing employee policies
banning talking and texting while driving.

– Public opinion polls show a majority of the
public support these efforts.

But there’s a troubling common thread
to these prevention efforts:
– Nearly all legislation focuses on banning only
handheld phones or only texting while driving.

– All state laws and many employer policies allow
hands-free cell phone use.

– Public opinion polls show people recognize the
risks of talking on handheld phones and texting
more than they recognize the risks of handsfree
phones.

– Many drivers mistakenly believe talking on a
hands-free cell phone is safer than handheld.

A hands-free device most often is a headset that
communicates via wire or wireless with a phone, or
a factory-installed or aftermarket feature built into
vehicles that often includes voice recognition. Many
hands-free devices allow voice-activated dialing
and operation.

Hands-free devices often are seen as a solution
to the risks of driver distraction because they help
eliminate two obvious risks – visual, looking away
from the road and manual, removing your hands
off of the steering wheel. However, a third type of
distraction can occur when using cell phones while
driving – cognitive, taking your mind off the road.

Hands-free devices do not eliminate
cognitive distraction.

The amount of exposure to each risk is key. Crashes
are a function of the severity of each risk and how
often the risk occurs. Most people can recognize
when they are visually or mechanically distracted
and seek to disengage from these activities as
quickly as possible. However, people typically do not
realize when they are cognitively distracted, such as
taking part in a phone conversation; therefore, the
risk lasts much, much longer. This likely explains
why researchers have not been able to find a safety
benefit to hands-free phone conversations.

The National Safety Council has compiled more than
30 research studies and reports by scientists around
the world that used a variety of research methods,
to compare driver performance with handheld and
hands-free phones. All of these studies show handsfree
phones offer no safety benefit when driving. Conversation
occurs on both handheld and hands-free phones. The cognitive
distraction from paying attention to conversation – from
listening and responding to a disembodied voice –
contributes to numerous driving impairments.
Specific driving risks are discussed in detail later in
this paper. First, let us look at why hands-free and
handheld cell phone conversations can impair your
driving ability.

Multitasking: A brain drain

This section provides the foundation to understand
the full impact of driving while engaging in cell phone
conversations on both handheld and hands-free
phones. It explains how cognitively complex it is to
talk on the phone and drive a vehicle at the same
time, and why this drains the brain’s resources.

Multitasking is valued in today’s culture, and our
drive for increased productivity makes it tempting to
use cell phones while behind the wheel. People often
think they are effectively accomplishing two tasks at
the same time. And yes, they may complete a phone
conversation while they drive and arrive at their
destination without incident, thus accomplishing two
tasks during the same time frame. However, there
are two truths to this common belief.

1. People actually did not “multitask.”
2. People did not accomplish both tasks with
optimal focus and effectiveness.

Multitasking is a myth. Human brains do not
perform two tasks at the same time. Instead, the
brain handles tasks sequentially, switching between
one task and another. Brains can juggle tasks
very rapidly, which leads us to erroneously
believe we are doing two tasks at the same time.
In reality, the brain is switching attention between
tasks – performing only one task at a time.

In addition to “attention switching,” the brain
engages in a constant process to deal with the
information it receives:

1. Select the information the brain will attend to
2. Process the information
3. Encode, a stage that creates memory
4. Store the information.

Depending on the type of information, different
neural pathways and different areas of the brain are
engaged. Therefore, the brain must communicate
across its pathways.

Furthermore, the brain must go through two more
cognitive functions before it can act on saved
information. It must:

5. Retrieve stored information
6. Execute or act on the information.

When the brain is overloaded, all of these steps are
affected. But people may not realize this challenge
within their brains.

The brain not only juggles tasks, it also juggles
focus and attention. When people attempt to
perform two cognitively complex tasks such as
driving and talking on a phone, the brain shifts its
focus (people develop “inattention blindness”) (page
9). Important information falls out of view and is not
processed by the brain. For example, drivers may
not see a red light. Because this is a process people
are not aware of, it’s virtually impossible for people
to realize they are mentally taking on too much.

When we look at a view before us – whether we are
in an office, restaurant or hospital, at the beach, or
driving in a vehicle – we believe we are aware of
everything in our surroundings. However, this is not
the case. Very little information actually receives full
analysis by our brains. Research shows we are blind
to many changes that happen in scenery around
us, unless we pay close and conscious attention
to specific details, giving them full analysis to get
transferred into our working memory.

Brain researchers have identified “reaction-time
switching costs,” which is a measurable time
when the brain is switching its attention and focus
from one task to another. Research studying the
impact of talking on cell phones while driving has
identified slowed reaction time to potential hazards
are tangible, measurable and risky (page 10). Longer
reaction time is an outcome of the brain switching
focus. This impacts driving performance.

The cost of switching could be a few tenths of
a second per switch. When the brain switches
repeatedly between tasks, these costs add up.

Even small amounts of time spent switching can lead
to significant risks from delayed reaction and braking
time. For example, if a vehicle is traveling 40 mph, it
goes 120 feet before stopping. This equals eight car
lengths (an average car length is 15 feet). A fractionof-
a-second delay would make the car travel several
additional car lengths. When a driver needs to react
immediately, there is no margin for error.

Brains may face a “bottleneck” in which different
regions of the brain must pull from a shared and
limited resource for seemingly unrelated tasks,
constraining the mental resources available for the
tasks. Research has identified that even when
different cognitive tasks draw on two different
regions of the brain, we still can have performance
problems when trying to do dual tasks at the same
time. This may help explain why talking on cell
phones could affect what a driver sees: two usually
unrelated activities become interrelated when a
person is behind the wheel. These tasks compete for
our brain’s information processing resources. There
are limits to our mental workload.

The workload of information processing can
bring risks when unexpected driving hazards
arise. Under most driving conditions, drivers are
performing well-practiced, automatic driving tasks.
For example, without thinking about it much, drivers
slow down when they see yellow or red lights, and
activate turn signals when intending to make a
turn or lane change. These are automatic tasks for
experienced drivers. Staying within a lane, noting
the speed limit and navigation signs, and checking
rear- and side-view mirrors also are automatic
tasks for most experienced drivers. People can do
these driving tasks safely with an average cognitive
workload. During the vast majority of road trips,
nothing bad happens, as it should be. But that also
can lead people to feel a false sense of security or
competency when driving. Drivers may believe they
can safely multitask; however, a driver always must
be prepared to respond to the unexpected.

Multitasking impairs performance

A driver’s response to sudden hazards, such as
another driver’s behavior, weather conditions, work
zones, animals or objects in the roadway, often
is the critical factor between a crash and a nearcrash.
When the brain is experiencing an increased
workload, information processing slows and a driver
is much less likely to respond to unexpected hazards
in time to avoid a crash.

The industrial ergonomics field has been able to
identify physical workload limits and, in the same
way, the workload limits of our brains now are being
identified. The challenge to the general public is the
bottlenecks and limits of the brain are more difficult
to feel and literally see than physical limits.

Multitasking Impairs Performance

We can safely walk while chewing gum in a city
crowded with motor vehicles and other hazards.
That is because one of those tasks – chewing gum –
is not a cognitively demanding task.
When chewing gum and talking, people still
are able to visually scan the environment for
potential hazards:
– Light poles along the sidewalk
– Boxes suddenly pushed out a doorway at
ground level before the delivery man emerges
– Moving vehicles hidden by parked vehicles
– Small dog on a leash
– Uneven sidewalk

People do not perform as well when trying to
perform two attention-demanding tasks at the
same time. Research shows even pedestrians
don’t effectively monitor their environment for
safety while talking on cell phones. The challenge
is managing two tasks demanding our cognitive
attention.

Certainly most would agree that driving a vehicle
involves a more complex set of tasks than walking.

The brain is behind all tasks needed for driving:
visual, auditory, manual and cognitive. Recent
developments in functional magnetic resonance
imaging (fMRI) now allow researchers to see the
brain’s reactions to specific challenges and tasks.

A Carnegie Mellon University study produced fMRI
pictures of the brain while study participants drove
on a simulator and listened to spoken sentences
they were asked to judge as true or false.36 The
pictures below show that listening to sentences on
cell phones decreased activity by 37 percent in the
brain’s parietal lobe, an area associated
with driving. In other words, listening and language
comprehension drew cognitive resources away
from driving. This area of the brain is important
for navigation and the type of spatial processing
associated with driving. Because this study
involved listening and thinking of an answer
and not actual cell phone conversation,
the researchers concluded the results may
underestimate the distractive impact of
cell phone conversation.

The same study also found decreased activity in the
area of the brain that processes visual information,
the occipital lobe. While listening to
sentences on cell phones, drivers had more
problems, such as weaving out of their lane and
hitting guardrails. This task did not require holding
or dialing the phone, and yet driving performance
deteriorated. The scientists concluded this study
demonstrates there is only so much the brain
can do at one time, no matter how different the
two tasks are, even if the tasks draw on different
areas and neural networks of the brain. The brain
has a capacity limit. These fMRI images provide a
biological basis of the risks faced by drivers.

Driving risks of hands-free and handheld cell phones

We now understand how our brains have difficulty
juggling multiple cognitive tasks that demand our
attention. Next we will discuss specific risks that cell
phone conversations bring to driving, with an overview
of crash risks and driver errors most often associated
with both hands-free and handheld cell phones.

Inattention Blindness – Vision is the most important
sense we use for safe driving. It’s the source of the
majority of information when driving. Yet, drivers
using hands-free and handheld cell phones have
a tendency to “look at” but not “see” objects.
Estimates indicate drivers using cell phones look at
but fail to see up to 50 percent of the information
in their driving environment. Cognitive distraction
contributes to a withdrawal of attention from the
visual scene, where all the information the driver
sees is not processed. This may be due to the
earlier discussion of how our brains compensate for
receiving too much information by not sending some
visual information to the working memory. When
this happens, drivers are not aware of the filtered
information and cannot act on it.

Distracted drivers experience inattention blindness.
They are looking out the windshield, but do not
process everything in the roadway environment
necessary to effectively monitor their surroundings,
seek and identify potential hazards, and to respond
to unexpected situations. Their field of view
narrows. To demonstrate this, Figure 4 is a typical
representation of where a driver would look while not
using a phone. Figure 5 shows where drivers looked
while talking on hands-free cell phones.

Drivers talking on hands-free cell phones are more
likely to not see both high and low relevant objects,
showing a lack of ability to allocate attention to the
most important information. They miss visual cues
critical to safety and navigation. They tend to miss
exits, go through red lights and stop signs, and
miss important navigational signage. Drivers on
cell phones are less likely to remember the content
of objects they looked at, such as billboards.
Drivers not using cell phones were more likely
to remember content.

The danger of inattention blindness is that when
a driver fails to notice events in the driving
environment, either at all or too late, it’s impossible
to execute a safe response such as a steering
maneuver or braking to avoid a crash.

To explore how cell phone use can affect driver visual
scanning, Transport Canada’s Ergonomics Division
tracked the eye movements of drivers using handsfree
phones, and again when these drivers were not
on the phone. In addition to looking
less at the periphery, drivers using hands-free phones
reduced their visual monitoring of instruments and
mirrors, and some drivers entirely abandoned those
tasks. At intersections, these drivers made fewer
glances to traffic lights and to traffic on the right.
Some drivers did not even look at traffic signals.

Slower Response Time and Reaction Time –
Response time includes both reaction time and
movement time. Reaction time involves attentional
resources and information processing, while
movement time is a function of muscle activation.
Cell phone use has been documented to affect
reaction time.

Due to the “attention switching” costs discussed
earlier, it makes sense that driver reactions may be
slower when using cell phones. For every information
input, the brain must make many decisions: whether
to act on information processed, how to act,
execute the action and stop the action. While this
process may take only a fraction of a second, all of
these steps do take time. When driving, fractions
of seconds can be the time between a crash or no
crash, injury or no injury, life or death.

Numerous studies show delayed response and
reaction times when drivers are talking on hands-free
and handheld cell phones. Reaction
time has shown impairment in a variety of scenarios:

– A University of Utah driving simulator study
found drivers using cell phones had
slower reaction times than drivers impaired by
alcohol at a .08 blood alcohol concentration,
the legal intoxication limit. Braking time also
was delayed for drivers talking on hands-free
and handheld phones.

– Drivers talking on hands-free phones in
simulated work zones took longer to reduce
their speed when following a slowing vehicle
before them and were more likely to brake hard
than drivers not on the phone. Many braking
scenarios included clues that traffic was
going to stop. Side-swipe crashes also were
more common. Work zones are challenging
environments for all drivers, and rear-end
collisions are a leading type of work zone
crash, putting workers and vehicle occupants
at risk. Driver distraction is a significant
contributing factor to work zone crashes.

– Hands-free phone use led to an increase in
reaction time to braking vehicles in front of
drivers, and reaction time increased more and
crashes were more likely as the traffic density
increased.

Drivers in reaction time studies tended to show
compensation behaviors by increasing following
distance. However, drivers in three studies who
attempted to compensate for their reduced attention
this way found increased headway often was not
adequate to avoid crashing.

Problems Staying in Lane – “Lane keeping” or
“tracking” is the driver’s ability to maintain the
vehicle within a lane. While most cell phone driver
performance problems involve significant reaction
time impairment, there are minor, less significant
costs with lane keeping. It is suggested that lane
keeping may depend on different visual resources
than responding to hazards by reacting. In addition,
avoiding hazards requires drivers to watch for
unexpected events, choose an appropriate response
and act. This requires information processing and
decision-making that is more cognitively demanding
than lane keeping tasks, which is more automatic.

Still, when we are driving at roadway and freeway
speeds with vehicles spaced less than a few feet
from each other in parallel lanes, the margin of error
for decision-making and response time to avoid a
crash is very small. Perhaps drivers who create a
hazard by straying from their lanes must depend on
other drivers around them to drive defensively and
respond appropriately, and it may be those reacting
drivers whose cell phone use should be of concern.

Recent naturalistic studies, have reported a
risk of crashing while talking on a cell phone to
be significantly less than the fourfold risk found
in the above epidemiological studies. This new
methodology, although offering great promise
in the endeavor to understand what really goes
on in a vehicle prior to a crash, has significant
limitations, including:

– Very small number of observed crashes.
– The use of “near-crash” data to calculate
crash risk.
– Inability to collect all near-crash occurrences.
– Inability to observe or measure cognitive
distraction.
– Inability to observe hands-free phone use.

All methodologies have strengths and significant
limitations. There is no “gold standard” of research
methodology. Each research method provides
valuable knowledge. In this case, experimental
studies have been used to measure the risks of
cognitive distraction, because other methods,
particularly naturalistic research methods, cannot
effectively measure it. In making decisions about
laws, vehicle and roadway improvements, and driver
behavior, the entire body of research should always
be considered. When doing so, it is clear that the risk
of crashing when engaged in a hands-free phone
conversation is about 4 times greater than when not
using a phone while driving.

Are drivers able to reduce their own risk?

There is evidence that people are aware of
distracted driving risks to drivers, in general. In a
AAA Foundation for Traffic Safety survey, 83 percent
of respondents said drivers using cell phones is a
“serious” or “extremely serious” problem. It was
rated a serious or extremely serious problem more
often than aggressive drivers, excessive speeding
and running red lights. Only alcohol-impaired driving
was rated as a serious problem by more people.
But do these people recognize their own risks of
using cell phones while driving? Despite their stated
belief in the dangers, more than half of the same
survey respondents reported talking on cell phones
while driving during the previous 30 days. Seventeen
percent admitted this behavior “often” or “very often.”

Furthermore, due to how our brains filter information,
as discussed earlier, we are never aware of the
information that was filtered out. This may add
to the lack of awareness of our limitations. Some
researchers have studied whether distracted
drivers are aware of their decrease in safe driving
performance. Findings show distracted drivers may
not be aware of the effects of cognitive distraction
and using cell phones while they are driving.
Also, drivers perceived they were safer drivers when
using hands-free phones, but actually showed
decreased performance while using hands-free
phones. One study found drivers who thought
the task was easy tended to perform the worst.

It is well-known from many traffic safety issues
with a long history of injury prevention strategies
– impaired driving, teen driving, speeding, safety
belts and child safety seats – that even when people
are aware of the risks, they may not easily change
behaviors to reduce the risk.

What are possible prevention steps?

Eliminating driver distraction due to cell phone use
faces significant challenges, even beyond combating
drivers’ desire to be connected and productive.
Drivers can help avoid this by informing frequent
callers that they will not participate in phone
conversations while driving. When facing multiple
demands for their cognitive attention, drivers
may not be aware they are missing critical visual
information, and they may not be aware of the full
impact of that oversight. This lack of awareness
of the distraction could prolong it. Widespread
education is needed about the risks of hands-free
devices, conversation and cognitive distraction.

There is a shared responsibility among all involved in
cell phone conversations to avoid calling and talking
while driving – including drivers, callers and the
people that drivers may call. Vehicle manufacturers
are including more wireless and voice recognition
communications technologies in vehicles, but their
impact on distraction has yet to be fully studied.
Consumers should consider their exposure to
cognitive distraction and increased crash risk while
using these in-vehicle technologies.

But even when people are aware of the risks, they
tend to believe they are more skilled than other
drivers, and many still engage in driving behaviors
they know are potentially dangerous. Prevention
strategies should consider how people behave in
reality, not only how they should behave. We know
from other traffic safety issues – impaired driving,
safety belts, speeding – that consistent enforcement
of laws is the single most important effective
strategy in changing behavior. Therefore, prevention
strategies that may show the most promise are
legislative and corporate policies, coupled with
high-visibility enforcement and strict consequences.
Technology solutions can go even further by
preventing calls and messages from being sent or
received by drivers in moving vehicles. To provide
safety benefits and provide a positive influence on
reducing crashes, injuries and deaths, these efforts
– including education, policies, laws and technology
– must address the prevention of both handheld and
hands-free cell phone use by drivers.